A major challenge in cancer treatment is to target specific therapies to distinct tumor types in order to maximize efficacy and minimize toxicity. Meeting this challenge requires that physicians and others involved in the treatment of cancer patients be able to identify distinct tumor types, determine the likelihood of patient survival given the patient's distinct tumor type, and be able to select appropriate treatments.
In the oncology field it is currently standard practice to identify tumor types using the microscopic histopathologic appearance of fixed and stained tumor samples, and to utilize the tumor-node-metastasis (TNM) system to determine the clinical extent of tumor spread. The TNM system uses the size of the tumor, the presence or absence of tumors in regional lymph nodes, and the presence or absence of distant metastases to assign a stage to the tumor. The tumor type and the stage assigned to a tumor are used as a basis for the selection of appropriate therapy and for prognostic purposes. However, this approach has serious limitations. This is because tumors with similar histopathologic appearance can exhibit significant variability in terms of clinical course and response to therapy. For example, some tumors spread early to distant sites and are rapidly progressive while others are not, and some tumors respond readily to hormonal therapy or chemotherapy while others are resistant.
Basal-like breast cancer tumors are one example of a tumor type that grows rapidly and which typically are not treated effectively with conventional adjuvant therapies such as hormonal therapy or chemotherapy. Clinically, basal-like breast cancers behave aggressively, and while they may respond to chemotherapy initially, these responses are generally of brief duration, and survival times for most patients with these tumors are relatively short. Histologically, most basal-like breast cancers are poorly differentiated ductal carcinomas. Breast cancer tumors are normally classified as basal-like in the clinical setting based on whether the tumors have a so-called “triple-negative” phenotype characterized by a lack of over-expression of human epidermal growth factor receptor 2 (HER2), the estrogen receptor (ER), and the progesterone receptor (PR) and if the tumor over-expresses basal-like cytokeratins or other basal-like markers. Unfortunately, therapeutic options for patients with basal-like breast cancers are limited, because patients with such tumors are not candidates for hormonal therapy or targeted therapy against HER2 and there currently is no clear understanding of the underlying pathobiology of basal-like breast cancers. Importantly, basal-like tumors and distinct subsets of such tumors may also arise in other tissues and organs such as lung, thyroid, ovarian, and prostate tissues, but this has been poorly studied.
Furthermore, many tumors have aberrations in the expression or biological activity of proteins encoded by tumor suppressor genes. Aberrations in the biological activity of proteins encoded by tumor suppressor genes due to mutations in these genes or decreased gene transcription at the level of mRNA or protein expression can lead to unrestrained cell division. The Rb protein is an example of a protein encoded by a tumor suppressor gene. Normally, the Rb tumor suppressor protein binds to the E2F transcription factor and regulates E2F mediated gene transcription to negatively modulate and control cell proliferation. Importantly, the role of Rb and E2F in basal-like tumors in breast tissues and other tissues such as lung, thyroid, ovarian, and prostate tissues is also poorly understood.
Thus, there is a need for methods to identify tumors that over-express E2F responsive genes, methods for determining the likelihood that a patient diagnosed with a particular distinct tumor type will survive to a future date, methods for identifying and treating distinct tumor types, and methods for identifying target proteins expressed by a distinct tumor type in different tissues such as breast, lung, thyroid, ovarian prostate and other tissues.